1. Field of the Invention
The present invention is related to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and a method of handling a device-to-cellular (D2C) communication in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Different from the LTE/LTE-A system operating in a frequency-division duplexing (FDD) mode (or simply FDD system), transmission directions of subframes of a frequency band in the LTE/LTE-A system operating in a time-division duplexing (TDD) mode (or simply TDD system) may be different. That is, the subframes in the same frequency band are divided into UL subframes, downlink (DL) subframes and special subframes according to the UL/DL configuration specified in the 3GPP standard.
FIG. 1 is a table 10 of the UL/DL configurations with subframes and corresponding directions according to the prior art. In FIG. 1, 7 UL/DL configurations are shown, wherein each of the UL/DL configurations indicates a set of transmission directions (hereinafter, directions, for short) for 10 subframes, respectively. Each subframe is indicated with a corresponding subframe number (i.e., subframe index) in FIG. 1. In detail, “U” represents that the subframe is a UL subframe where UL data is transmitted, and “D” represents that the subframe is a DL subframe where DL data is transmitted. “S” represents that the subframe is a special subframe where control information and maybe data (according to the special subframe configuration) is transmitted.
Device-to-device (D2D) communication may be realized, after an initialization (e.g., connection establishment and/or peer discovery) is performed (e.g., assisted by an eNB). Then, two UEs may communicate (e.g., transmitting and/or receiving packets) with each other (e.g., directly) according to the D2D communication, and the eNB may not need to forward the packets transmitted between the UEs. According to the D2D communication, the UEs may communicate with each other via UL resources (e.g., UL subframes configured by the eNB). In general, the D2D communication may also be seen as a D2D service (i.e., proximity-based service (ProSe)). The D2D service can be a ProSe direct discovery or a ProSe direct communication. In addition, a D2D subframe, D2D transmission, D2D communication and D2D discovery can be termed as a sidelink subframe, sidelink transmission, sidelink communication and sidelink discovery, respectively.
According to the currently developed 3GPP standard, frequency-division multiplexing (FDM) between a D2D communication and a device-to-cellular (D2C) communication is not allowed for a FDD system. The D2C communication and the D2D communication may occur in a same subframe of a same carrier. That is, a UE may be scheduled to perform a D2C transmission and a D2D transmission in the same subframe of the same carrier. The collision between the D2C transmission and the D2D transmission may be resolved according to a proper arrangement of resources. However, the D2C transmission and the D2D transmission may not be performed efficiently due to inefficient usage of the resources and characteristics of the FDD system, even though the collision is resolved. Accordingly, throughputs of the UE and the eNBs are limited.
Thus, how to solve resource allocation for the D2C communication and the D2D communication in the FDD system is an important topic to be discussed.